The major objective of the proposed research is to understand the structural basis for the functional differences observed in human paraoxonase (PON1) genetic variants. We have partially characterized the effects of five coding region polymorphisms and five upstream regulatory polymorphisms. The Q192R polymorphism affects the catalytic efficiency of PON1 for hydrolysis of a number of substrates, while the position -108C/T polymorphism affects PON1 expression. Three newly discovered polymorphisms result in inactive PON1 alleles. Our goal is to understand the functional genomics of these polymorphisms. We will use a PON1 mouse model to examine the effects of acute exposure to organophosphorus (OP) compounds. The mouse model includes PON1 knockout mice as well as knockout mice expressing one or more copies of each human PON1-Q192R allele. This model system will allow us to test the hypothesis that a polymorphic PON1-Q192R allele expressed at a given level will provide a specific degree of resistance to the toxicity of environmental agents hydrolyzed directly by PON1 or metabolized through the cytochrome P450 /PON1 pathway. The model will also allow us to investigate the effects of PON1 polymorphisms in modulating the effects of low level OP exposure on gene expression in the brain, an area of research that has not been previously approachable. We propose to investigate five facets of PON1 genetic variability that will provide information on the functional genomics of the polymorphisms of the human PON1 gene. Specific aim 1 examines the toxicological effects of acute exposures of diazoxon (DZO), chlorpyrifos oxon (CPO) and chlorpyrifos (CPS) on mice whose PON1 genes have been replaced with one or two copies of human PON1 Q192 or R192.Specific aim 2 examines the modulating effects of the PON192 variants on the toxicogenomic expression profile of genes in the affected subregions/cells of brains of PON1-192 transgenic mice exposed to CPO and DZO. Specific aim 3 is aimed at identifying new protein targets modified by exposure to CPO. Specific aim 4 involves determination of the crystal structure of human PON1 and characterization of recombinant PON1 variants with increased efficiency of OP hydrolysis. Specific aim 5 involves development of a human pharmacokinetic/pharmacodynamic (PDPK/PD) model of organophosphate exposure using humanized transgenic PON1 knockout mice expressing varying levels of each human PON1-192 isoform.